A beautiful, responsive, customisable, accessible (WAI-ARIA) replacement for JavaScript's Popup boxes with zero dependencies, SweetAlert2 automatically centers itself on the page and looks great no matter if you're using a desktop computer, mobile or tablet. It's even highly customisable, as you can see below!

A set of effects for modals created with CSS. They animate thanks to CSS transforms and animations that are supported by several modern browsers, a...

A set of effects for modals created with CSS. They animate thanks to CSS transforms and animations that are supported by several modern browsers, and some effects use SVG animations of morphing paths with the help of Snap.svg. The resource is free and it comes with an article explaining the process.